Direct detection of influenza virus antigen in nasopharyngeal specimens by direct enzyme immunoassay in comparison with quantitating virus shedding

Abstract

We developed a direct enzyme immunoassay [EIA; Enzygnost Influenza A(Ag) and Enzygnost Influenza B(Ag)] for the direct detection of influenza A and B virus antigens in nasopharyngeal secretion specimens (NPS). The test is performed without sonification of specimens, and results are obtained within 4 h. A direct comparison between direct EIA and quantitation of virus shedding for influenza A and B virus antigen detection was carried out. A total of 210 NPS and 98 nasopharyngeal wash specimens (NPW) were investigated. We isolated influenza A viruses from 79 (37.6%) of 210 NPS; of these 79 cell-culture-positive NPS, 70 (88.6%o) were also positive by direct EIA. Of 29 (13.8%) NPS from which influenza B virus was isolated, 24 (82.8%) NPS were positive by direct EIA. Virus shedding was determined quantitatively in 48 NPS from patients with influenza A and in 24 NPS from patients with influenza B. Only a crude correlation between optical density values and virus concentrations was observed. Detection of influenza virus antigens in NPS by direct EIA showed sensitivities of 89.7% for influenza A virus and 87.9%o for influenza B virus and specificities of 99.3% for influenza A virus and 100% for influenza B virus. With direct ETA, all NPW were negative for influenza A virus, although virus was isolated from 21 (21.4%) NPW. Of 15 NPW from which influenza B virus was isolated, 7 showed positive results in direct EIA. In addition, direct EIA is suitable for detecting influenza A and B viruses in cell cultures before the appearance of any cytopathic effects and can be used as a cell culture confirmation test.

Influenza Pneumonia

“…It is unlikely that false-positive results were included in our series since specificities for the rapid viral tests are high (range, 90 to 99%). [5][6][7][8][9] It is more likely that the total number of influenza cases was underestimated, because sensitivities can be as low as 65% (range, 65 to 96%). In our study, rapid diagnosis was helpful in the institution of antiviral treatment and control measures, such as respiratory isolation.…”

Chinese herbs in treatment of influenza: A randomized, double-blind, placebo-controlled trial

“…Influenza was confirmed by a direct immunofluorescent antibody assay (DFA) of nasopharyngeal swabs, which showed sensitivities of 89.7% for influenza A virus and 87.9% for influenza B virus and specificities of 99.3% for influenza A virus and 100% for influenza B virus. 16 Treatment assignment was blinded during virological testing, which was done at West China Hospital, Sichuan University, Chengdu.…”

Simultaneous Detection of Influenza Viruses A and B Using Real-Time Quantitative PCR

“…Alternative diagnostic techniques, such as viral antigen de-tection (immunofluorescence and enzyme immunoassay techniques) and shell vial culturing, on the other hand, provide results much more quickly but generally are less sensitive than conventional cell culturing (4,11,15,18,20).…”